First-principles calculations of MnB2, TcB2, and ReB2 within the ReB2-type structure

The structural, mechanical, and electronic properties of MnB2, TcB2, and ReB2 have been studied by performing first-principles calculations at the level plane-wave basis pseudopotential formalism in both aluminum diboride-and rhenium diboride-type structures. The results of local density approximation and generalized gradient approximation indicated that all three of hexagonal structures within rhenium diboride-type are energetically favorable than those of aluminum diboride-type, they are mechanically stable and also hard materials. In addition to electronic properties of highly directional covalent bonds, optimal filling of bonding states, mechanical properties, and also the Debye temperature of the structures support that the rhenium diboride-type hexagonal phase of MnB2 is harder than the others. Interestingly, instead of other five structures, only MnB2 within aluminum diboride-type hexagonal structure has a finite magnetic moment at the equilibrium geometry.